1. Field of the Invention
The present invention relates to a simple and economical process for the preparation of an intermediate pitch which is suitable for the production of a variety of carbon products and particularly carbon fibers, from a heavy oil of petroleum or coal origin. More particularly, the present invention relates to a process for a continuous preparation of an intermediate pitch for manufacturing carbon products which comprises heating a heavy oil of a petroleum or coal origin in a tubular heater at a specific pressure, temperature and residence time; transfering the heater effluent to a flash distillation column and conducting flash distillation at a specific pressure and temperature so as to separate lighter fractions from heavy fraction and recovering the heavy fraction as the intermediate pitch.
Carbon products are important as structure materials, and carbon fibers in particular are very important as components of composite materials.
2. Description of the Prior Arts
Carbon fibers have hetherto been produced by carbonization of polyacrylonitrile (PAN) fibers. However, PAN fibers are expensive, the carbonization yields are low, and the carbon fibers produced by this process do not have satisfactory modulus. Attempts to raise their modulus by graphitization by high temperature treatment have been made but, unexpectedly, they resulted in a decreased modulus of the products.
As a result, many processes have been proposed which would allow production of pitches for spinning, which may be convertible to high strength carbon fibers in high carbonization yields, from inexpensive pitches originated from petroleum or coals.
For example, Japanese Patent Disclosure No. 214531/1983 discloses a process for preparing pitches for spinning by hydrogenation and subsequent thermal treatment of raw pitches, and Japanese Patent Disclosure No. 160427/1979 discloses a process for preparing pitches for spinning which comprises isolating isotropic pitches by solvent extraction of raw pitches and then conducting thermal treatment. However, when such processes are applied to raw pitches produced by conventional methods such as distillation, these processes are uneconomical because a large quantity of raw pitches should be treated due to low yields of carbon fibers. Moreover, the strength of the carbon fibers thus produced can not be regarded as sufficiently high: they generally show tensile strengths in the order of 200 Kg/mm.sup.2 and Young's modulus of 15-20 ton/mm.sup.2.